1. Field of the Invention
The present invention relates to a vacuum pump in which a rotor is supported by a ball bearing.
2. Description of the Related Art
Conventionally, there has been known a vacuum pump in which a rotor shaft of a rotor is supported by a ball bearing lubricated with grease. In such a vacuum pump, vibration is generated by whirling due to unbalance of the rotor, and the vibration is disadvantageously transmitted to the outside of the pump. As a countermeasure, there is a method of elastically supporting the ball bearing to damp the vibration.
For example, in a turbo-molecular pump described in WO 2006/131694, an inner sleeve which holds an outer ring of a ball bearing is held by an outer sleeve and the outer sleeve is fixed to a base. Further, in this configuration, elastic bodies (O-rings) are disposed between the outer periphery of the outer ring and the inner sleeve and between the inner sleeve and the outer sleeve. Further, a gel layer formed of thermal conductive gel is provided for improving the heat radiation performance between the inner sleeve and the outer sleeve. The gel layer is sealed with the elastic bodies.
However, when the ball bearing is elastically supported, it is necessary to sufficiently reduce the elastic modulus in order to sufficiently damp vibration transmitted to the outside of the pump. Thus, in the configuration as described in WO 2006/131694, that is, the configuration in which the gel layer is provided in a clearance in the radial direction between the inner sleeve and the outer sleeve, the support stiffness in the radial direction cannot be sufficiently reduced due to the influence of the gel layer.